Lead-based stack fuel element

Abstract

The embodiment of the invention relates to the technical field of fuel elements with devices for improving heat transfer efficiency, in particular to a lead-based stack fuel element which comprises a cladding, a fuel core block and an elastic heat transfer part. The fuel pellet is arranged in the cladding, and an annular gap is formed between the fuel pellet and the cladding in the radial direction of the cladding. The elastic heat transfer piece is arranged in the annular gap and arranged to be capable of being in heat conduction contact with the fuel pellet and the cladding at the same time so as to conduct heat of the fuel pellet to the cladding, and the elastic heat transfer piece can elastically deform to adapt to swelling of the fuel pellet. According to the lead-based reactor fuel element, a heat transfer path between the fuel pellet and the cladding can be established, heat of the fuel pellet can be conveniently transferred to the cladding to exchange heat with a coolant, the temperature difference between the cladding and the fuel pellet is reduced, meanwhile, the damage risk of the cladding is reduced, the structural integrity of the fuel element is ensured, and the service life of the fuel element is prolonged. And therefore, the safety performance of the lead-based reactor is effectively improved, and the lead-based reactor can run under higher power density.

Description

TECHNICAL FIELD

[0001] Embodiments of the present application relate to the technical field of fuel elements with devices for improving heat transfer efficiency, and in particular to a lead-based reactor fuel element. BACKGROUND

[0002] The statements herein are merely provided to give a basic understanding of the present application and are not necessarily intended to constitute the prior art.

[0003] The fuel operating temperature of a nuclear reactor is closely related to its safety, and the temperature difference between the cladding and the fuel pellets is an important factor affecting the fuel operating temperature. The smaller the temperature difference between the cladding and the fuel pellets of the fuel element, the lower the operating temperature of the fuel, and the more conducive to the heat generated by the fuel pellets being transferred to the coolant, so that the negative feedback of the coolant can take effect in time, thereby improving the inherent safety of the reactor.

[0004] The size of the temperature difference between the cladding and the fuel pellets is associated with the structure of the fuel element. During operation, the fuel pellets will swell due to irradiation, and a certain gap needs to be reserved between the pellets and the cladding to accommodate the swelling space of the pellets. If the gap is insufficient, mechanical interaction between the fuel and the cladding may occur after the fuel swells, which may cause the cladding to break and radioactive leakage. In the usual design, the gap between the pellets and the cladding is filled with inert gas, which has low thermal conductivity. At present, there is no structure design suitable for the fuel element of the lead-based reactor to reduce the temperature difference between the cladding and the fuel pellets of the fuel element serving in the lead-based reactor, thereby reducing the fuel operating temperature and significantly affecting the operating safety of the lead-based reactor. SUMMARY

[0005] A brief summary of the present application is presented in the following to provide a basic understanding of some aspects of the present application. It should be understood that this summary is not an exhaustive overview of the present application. It is not intended to identify key or important parts of the present application nor is it intended to limit the scope of the present application. Its purpose is merely to present some concepts in a simplified form as a prelude to the more detailed description of a later discussion.

[0006] Embodiments of the present application provide a lead-based reactor fuel element, which comprises a cladding, a fuel pellet and an elastic heat transfer member. The fuel pellet is arranged in the cladding, and an annular gap is formed between the fuel pellet and the cladding along the radial direction of the cladding. The elastic heat transfer member is arranged in the annular gap and is arranged to be in thermal contact with the fuel pellet and the cladding to conduct heat from the fuel pellet to the cladding, and to be elastically deformed to accommodate the swelling of the fuel pellet.

[0007] The lead-based reactor fuel element in the embodiment of the present application sets the elastic heat transfer member in the annular gap formed between the fuel pellet and the cladding, and sets the elastic heat transfer member to be capable of being in thermal contact with the fuel pellet and the cladding to conduct the heat of the fuel pellet to the cladding, and being capable of being elastically deformed to adapt to the swelling of the fuel pellet to establish the heat transfer path between the fuel pellet and the cladding, so as to facilitate the heat transfer of the fuel pellet to the cladding to exchange heat with the coolant, thereby reducing the temperature difference between the cladding and the fuel pellet, and reducing the risk of damage to the cladding, ensuring the structural integrity of the fuel element, and further effectively improving the safety performance of the lead-based reactor, and facilitating the operation of the lead-based reactor at a higher power density. BRIEF DESCRIPTION OF DRAWINGS

[0008] Other purposes and advantages of the present application will be apparent and a more complete understanding can be obtained by referring to the following description of the embodiments of the present application taken in conjunction with the accompanying drawings.

[0009] Figure 1 is a sectional view of a lead-based reactor fuel element along a radial direction according to an embodiment of the present application;

[0010] Figure 2 is a sectional view of an elastic heat transfer member along a radial direction according to an embodiment of the present application;

[0011] Figure 3 is a sectional view of a lead-based reactor fuel element along a radial direction according to another embodiment of the present application;

[0012] Figure 4 is a sectional view of an elastic heat transfer member along a radial direction according to still another embodiment of the present application;

[0013] Figure 5 is Figure 1 is an enlarged view of region A in FIG. 4.

[0014] BRIEF DESCRIPTION OF DRAWINGS

[0015] 10, cladding; 11, annular gap; 20, fuel pellet; 30, elastic heat transfer member; 31, convex edge; 32, connecting edge.

[0016] It should be noted that the drawings are not necessarily drawn to scale, but are merely shown in a schematic manner so as not to affect the understanding of the reader. DETAILED DESCRIPTION

[0017] Exemplary embodiments of the present application will be described herein below with reference to the accompanying drawings. In the description, specific embodiments of the present application have not been described in all features for the sake of clarity and conciseness. It should be appreciated, however, that many embodiment-specific decisions must be made in order to implement any such actual embodiments, in order to achieve the specific goals of the developers, such as compliance with those constraints related to the system and business, which can vary from embodiment to embodiment. It should also be appreciated that, although the development work can be very complex and time-consuming, it is merely a routine task for those skilled in the art who benefit from the content of the present application.

[0018] It should also be noted herein that, in order to avoid obscuring the present application with unnecessary details, only the device structures and / or processing steps closely related to the scheme according to the present application are shown in the accompanying drawings, while other details less relevant to the present application are omitted.

[0019] In order to reduce the temperature difference between the cladding and the fuel pellets, the fuel elements serving in the sodium-cooled fast reactor adopt a structure of filling a liquid sodium bonding layer between the cladding and the fuel pellets, so as to effectively reduce the thermal resistance between the cladding and the fuel pellets, while being able to adapt to the swelling of the fuel pellets and maintain the integrity of the cladding.

[0020] As for the lead-based reactor, the inventors of the present application have found that this structure is not applicable to the fuel elements serving in the lead-based reactor, and if lead or lead bismuth is filled between the cladding and the fuel pellets, the lead or lead bismuth will severely corrode the fuel pellets under the high-temperature environment in the reactor, and the cladding will be subjected to double-sided corrosion, and since the melting point of lead or lead bismuth is high, the solidification and remelting of lead or lead bismuth will inevitably occur due to the change in ambient temperature during the manufacturing, assembly and loading and unloading of the fuel elements, which is not conducive to maintaining the integrity of the cladding, and therefore, there is still a technical gap in the structural design of the fuel elements of the lead-based reactor which can achieve a lower temperature difference between the cladding and the fuel pellets.

[0021] Based on this, the embodiments of the present application provide a lead-based reactor fuel element.

[0022] As shown in Figures 1 to 4 , Figure 1 and Figure 2 show the lead-based reactor fuel element of one embodiment of the present application and the radial cross-sectional view of the elastic heat transfer member of this embodiment, Figure 3 and Figure 4 show the lead-based reactor fuel element of another embodiment of the present application and the radial cross-sectional view of the elastic heat transfer member of this embodiment.

[0023] The lead-based reactor fuel element provided in the embodiments of this application includes: a cladding 10, fuel pellets 20, and an elastic heat transfer element 30. The fuel pellets 20 are disposed within the cladding 10, and an annular gap 11 is formed between the fuel pellets 20 and the cladding 10 along the radial direction of the cladding 10. The elastic heat transfer element 30 is disposed in the annular gap 11, configured to simultaneously conduct heat to both the fuel pellets 20 and the cladding 10 to transfer heat from the fuel pellets 20 to the cladding 10, and to elastically deform to accommodate the swelling of the fuel pellets 20.

[0024] The lead-based reactor fuel element provided in the embodiments of this application establishes a heat transfer path between the fuel pellet 20 and the cladding 10 by disposing an elastic heat transfer element 30 in the annular gap 11 formed between the fuel pellet 20 and the cladding 10. The elastic heat transfer element 30 is configured to simultaneously conduct heat to both the fuel pellet 20 and the cladding 10 to transfer heat from the fuel pellet 20 to the cladding 10, and to undergo elastic deformation to accommodate the swelling of the fuel pellet 20. This facilitates the transfer of heat from the fuel pellet 20 to the cladding 10 for heat exchange with the coolant, thereby reducing the temperature difference between the cladding 10 and the fuel pellet 20. At the same time, it reduces the risk of damage to the cladding 10, ensures the structural integrity of the fuel element, and thus effectively improves the safety performance of the lead-based reactor, enabling the lead-based reactor to operate at higher power densities.

[0025] In some embodiments, the elastic heat transfer element 30 is an annular metal foil, the diameter of the largest inscribed circle of the cross-section of the annular metal foil 30 is the same as the diameter of the fuel pellet 20, and the diameter of the smallest circumscribed circle of the cross-section of the annular metal foil 30 is the same as the inner diameter of the casing 10.

[0026] In this embodiment, the elastic heat transfer element 30 is set as an annular metal foil, with the diameter of its largest inscribed circle being the same as the diameter of the fuel pellet 20 and the diameter of its smallest circumscribed circle being the same as the inner diameter of the casing 10. This allows the elastic heat transfer element 30 to simultaneously achieve thermal contact with both the fuel pellet 20 and the casing 10, thereby establishing a heat transfer path between the fuel pellet 20 and the casing 10. This facilitates the transfer of heat from the fuel pellet 20 to the casing 10 and the coolant outside the casing 10 for heat exchange, thereby reducing the temperature difference between the casing 10 and the fuel pellet 20.

[0027] In some embodiments, the thickness of the annular metal foil 30 can be 10 μm to 100 μm.

[0028] like Figures 1 to 4 As shown, in some embodiments, the cross-section of the annular metal foil 30 includes a plurality of protruding edges 31 and a connecting edge 32 for connecting two adjacent protruding edges 31, wherein the connecting edge 32 is used to abut against the fuel pellet 20, and the protruding edges 31 are used to abut against the inner wall of the casing 10.

[0029] In the embodiment, the annular metal foil 30 is arranged to have a cross section comprising a plurality of convex edges 31 and connecting edges 32 connecting two adjacent convex edges 31, the connecting edges 32 are arranged to abut against the fuel pellets 20, and the convex edges 31 are arranged to abut against the inner wall of the cladding 10. When the fuel pellets 20 swell, the convex edges 31 and the connecting edges 32 can accommodate the deformation of the fuel pellets 20 and limit the fuel pellets 20 within the range surrounded by the convex edges 31 and the connecting edges 32. Since the thickness of the metal foil is very small, the metal foil itself does not substantially occupy the space of the annular gap 11, and even when the fuel pellets 20 swell to the extent close to the inner wall of the cladding 10, the annular metal foil 30 does not have a large tensile / compressive deformation in the circumferential direction of the cross section, thereby improving the adaptability of the annular metal foil 30 to the swelling of the fuel pellets 20, reducing the risk of damage to the cladding 10, and ensuring the structural integrity of the fuel element. In addition, each convex edge 31 and each connecting edge 32 abut against the fuel pellets 20 and the inner wall of the cladding 10, respectively, which facilitates positioning the fuel pellets 20 in the radial direction by the connecting edges 32 spaced apart along the circumferential direction of the fuel pellets 20, preventing the fuel pellets 20 from moving out of position in the radial direction and contacting the cladding 10, and further reducing the risk of damage to the cladding 10.

[0030] As shown in Figure 5 , Figure 5 is Figure 1 an enlarged view of the A area in FIG. 10. In some embodiments, the convex edges 31 can be curved surfaces with the same radius as the inner wall of the cladding 10, so that the convex edges 31 are in surface contact with the inner wall of the cladding 10. Surface contact can reduce stress and improve the structural strength of the annular metal foil 30, preventing deformation, while also enhancing the heat transfer coefficient and improving the heat transfer efficiency between the fuel pellets 20 and the cladding 10, thereby reducing the temperature difference between the fuel pellets 20 and the cladding 10.

[0031] In some embodiments, two adjacent convex edges 31 are connected by a connecting edge 32 in a smooth transition. In some embodiments, the radius of curvature of the convex edges 31 and the connecting edges 32 at any position is not less than 1 / 2 of the radius of the fuel pellets 20, thereby reducing the change rate of the circumference of the metal foil due to fuel swelling, thereby improving the adaptability of the annular metal foil 30 to the swelling of the fuel pellets 20. Under this premise, the contact surface of the connecting edges 32 when abutting against the fuel pellets 20 can be increased to reduce local stress.

[0032] In some embodiments, the cross section of the annular metal foil 30 can be a rotational symmetric structure, such that each convex edge 31 is equidistant from the position where it abuts against the inner wall of the cladding 10, and each connecting edge 32 is equidistant from the position where it abuts against the fuel pellet 20, so that the heat of the fuel pellet 20 is uniformly transferred to the cladding 10, which helps to improve the heat transfer efficiency, prevent the fuel pellet 20 from being locally overheated, and further reduce the temperature difference between the fuel pellet 20 and the cladding 10; at the same time, it more stably limits the positioning of the fuel pellet 20 and prevents the fuel pellet 20 from being in contact with the cladding 10 due to misalignment.

[0033] In some embodiments, the number of convex edges 31 can be 3 or 4. Since the fewer the convex edges 31, the farther the position where the convex edge 31 abuts against the inner wall of the cladding 10 and the position where the connecting edge 32 abuts against the fuel pellet 20, i.e., the longer the heat transfer path between the fuel pellet 20 and the cladding 10, but the simpler the structure; while the more the convex edges 31, the closer the position where the convex edge 31 abuts against the inner wall of the cladding 10 and the position where the connecting edge 32 abuts against the fuel pellet 20, i.e., the shorter the heat transfer path between the fuel pellet 20 and the cladding 10, but the more complex the structure, therefore, in the present embodiment, the number of convex edges 31 is set to 3 or 4, so as to ensure the heat transfer efficiency between the fuel pellet 20 and the cladding 10 while ensuring the simplicity of the annular metal foil structure.

[0034] In some embodiments, the material of the annular metal foil 30 can be molybdenum. Since molybdenum has high melting point, high thermal conductivity, low neutron absorption cross section, etc., and at the same time has good ductility, strength and toughness, and is easy to process, therefore, using molybdenum as the material for manufacturing the annular metal foil 30 is conducive to improving the heat transfer efficiency between the fuel pellet 20 and the cladding 10, further reducing the temperature difference between the fuel pellet 20 and the cladding 10, and at the same time enhancing the structural strength of the annular metal foil 30, further ensuring the structural integrity of the fuel element.

[0035] In some embodiments, the cladding 10 can be a circular tube structure composed of stainless steel or oxide dispersion strengthened steel (ODS), to jointly form the radioactive containment boundary of the fuel element with the end plugs on both sides, and provide certain structural strength to ensure the structural integrity of the fuel element. The inner surface of the cladding 10 is a smooth cylindrical surface.

[0036] In some embodiments, the fuel pellet 20 can be a cylindrical structure composed of one of uranium dioxide, uranium nitride, uranium carbide and metal alloy fuel, stacked along the axial direction of the cladding 10.

[0037] In some embodiments, helium gas is filled in the cladding 10. By filling the helium gas with high thermal conductivity in the cladding 10, the helium gas between the annular metal foil 30 and the fuel pellets 20 can transfer heat from the fuel pellets 20 to the annular metal foil 30, and the helium gas between the annular metal foil 30 and the cladding 10 can transfer heat from the annular metal foil 30 to the cladding 10, further enhancing the heat transfer efficiency between the fuel pellets 20 and the cladding 10, thereby further reducing the temperature difference between the fuel pellets 20 and the cladding 10. It is easily understood that the annular metal foil 30 is not sealed with the end plugs on both sides, and therefore the spaces on both sides of the annular metal foil 30 can be in gas communication at the end plugs, so that the helium gas can flow through the spaces on both sides of the annular metal foil 30.

[0038] For the embodiments of the present application, it also needs to be explained that the embodiments and the features in the embodiments of the present application can be combined with each other to obtain new embodiments without conflict.

[0039] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto, and the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A lead-based reactor fuel element, characterized in that, include: A casing and a fuel pellet disposed within the casing, wherein an annular gap is formed between the fuel pellet and the casing along the radial direction of the casing; An elastic heat transfer element is disposed in the annular gap and is configured to simultaneously make thermal contact with the fuel pellet and the cladding to conduct heat from the fuel pellet to the cladding, and to undergo elastic deformation to accommodate the swelling of the fuel pellet.

2. The lead-based reactor fuel element according to claim 1, characterized in that, The elastic heat transfer element is an annular metal foil. The diameter of the largest inscribed circle of the cross-section of the annular metal foil is the same as the diameter of the fuel pellet, and the diameter of the smallest circumscribed circle of the cross-section of the annular metal foil is the same as the inner diameter of the cladding.

3. The lead-based reactor fuel element according to claim 2, characterized in that, The cross-section of the annular metal foil includes multiple convex edges and connecting edges for connecting two adjacent convex edges, wherein the connecting edges are used to abut against the fuel pellet, and the convex edges are used to abut against the inner wall of the casing.

4. The lead-based reactor fuel element according to claim 3, characterized in that, The convex edge is a curved surface with the same radius as the inner wall of the casing.

5. The lead-based reactor fuel element according to claim 3, characterized in that, The cross-section of the annular metal foil has a rotationally symmetric structure.

6. The lead-based reactor fuel element according to claim 3, characterized in that, The number of protruding edges is 3 or 4.

7. The lead-based reactor fuel element according to claim 3, characterized in that, The radius of curvature at any position of the convex edge and the connecting edge is not less than 1 / 2 of the radius of the fuel pellet.

8. The lead-based reactor fuel element according to claim 2, characterized in that, The material of the ring-shaped metal foil is molybdenum.

9. The lead-based reactor fuel element according to claim 2, characterized in that, The thickness of the annular metal foil is 10 μm to 100 μm.

10. The lead-based reactor fuel element according to any one of claims 1-7, characterized in that, The fuel pellets are cylindrical structures composed of one of the following fuels: uranium dioxide, uranium nitride, uranium carbide, and metallic alloy fuels, stacked along the axial direction of the cladding; and / or The casing is filled with helium.

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